This invention is generally directed to processes for affecting the preparation of particles useful for incorporation into toner compositions. More specifically, the present invention is directed to dispersion polymerization processes for obtaining tough toner compositions that do not require jetting subsequent to the preparation thereof. Therefore, the process of the present invention relates to the preparation of polymer particles by the dispersion polymerization of monomers in the presence of known steric stabilizers and a crosslinking compound, which particles subsequent to being admixed with pigments are useful as toner compositions. The aforementioned toner compositions are of increased mechanical modulus derivable from sufficient polymer crosslinking; and further, there is obtained tone particles with a diameter of less than about 15 microns rendering it unnecessary to subject these particles to a jetting step as is affected in prior art processes. The toner compositions resulting from the process of the present invention are particularly useful for the development of images in electrostatic imaging processes wherein the imaging members selected can be positively or negatively charged.
The development of images, and in particular electrostatic images utilizing developing compositions with toner materials, is well known. In many of these processes, an electrostatic latent image that is formed on a photoconductor member is developed with a toner composition comprised of resin particles and carbon black. Subsequently, the developed image is transferred to a suitable substrate wherein fixing is accomplished by heat. Accordingly, final copies of the image are produced by heating the toner to a temperature at which it begins to flow enabling fusing thereof to a supporting substrate such as paper. Various suitable toner and developer compositions can be used in these processes. Recently, for example, there has been disclosed positively charged toners with charge enhancing additives, enabling their use in process wherein the imaging member is negatively charged. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium salts when incorporated into a toner provided a composition which exhibited relatively high uniform stable net toner charge when mixed with a suitable carrier vehicle.
There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Furthermore, there is disclosed in U.S. Pat. No. 4,338,390 developer and toner compositions having incorporated therein a charge enhancing additives organic sulfate and sulfonate compositions. Moreover, disclosed in U.S. Pat. No. 4,298,672 are positively charged toner compositions with resin and pigment particles; and as a charge enhancing additive alkyl pyridinium compounds.
Other patents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,143 and 4,394,430. Further, of interest with respect to crosslinked toner particles and polymerization processes for affecting the preparation thereof are U.S. Pat. Nos. 31072; 3,401,213; 3,941,898; 4,287,281; 4,448,871 and USSR Pat. No. 837,965.
Polymerization processes for obtaining toner compositions are also known. There is thus disclosed in U.S. Pat. No. 4,282,304 a suspension polymerization method wherein magnetic particles are first mixed with monomer together with an initiator, and subsequently the mixture is suspended in an aqueous medium where a reaction occurs within each particle. The aforementioned polymerization processes for obtaining toner compositions require monomers that are immiscible in the suspending medium, that is, a two phase system is present. Accordingly, the process described in the '304 patent selects a monomer and suspending medium that are mutually immiscible. Thus, the particle size control characteristics are an indirect property of the reacting system, and further the particle sizes generated are not a result of the mechanical dispersion processes as detailed in these patents. In other known dispersion polymerization processes, the monomer and suspending agents are initially miscible, thus a single phase system forms; however, the resulting polymer obtained subsequent to polymerization is insoluble in the mixture. The particle sizes of the particles obtained in the latter dispersion polymerization process is dependent upon the reacting components and their resulting aggregation behavior.
In a copending application U.S. Ser. No. 549,933 filed 11-9-83 now U.S. Pat. No. 4,524,199 entitled Stable Polymeric Dispersion and Methods for Making, the disclosure of which is totally incorporated herein by reference, there is described a stable polar dispersion, and a process thereof with nonionic amphipathic steric stabilizers irreversibly anchored to a monomer. Stabilizers disclosed in this copending application include hydroxyethyl cellulose.
Furthermore, in a related copending application U.S. Ser. No. 722,100, filed 4-11-85, entitled Toner Compositions and Dispersion Polymerization Process, the disclosure of which is totally incorporated herein by reference, there is disclosed dispersion by polymerization processes wherein the stabilizers selected are chemically treated. More specifically, there is provided in accordance with the invention of this copending application a dispersion polymerization process which comprises providing a medium having dispersed therein monodispersed particles comprised of a thermoplastic resin core which is substantially insoluble in the dispersion medium, irreversibly anchoring thereto certain stabilizers, and subsequently transforming the surface of the stabilizer by the reaction with compositions selected from the group consisting of alkyl halides, carboxylic acids, and aliphatic alcohols.
Also, there is disclosed in U.S. Pat. Nos. 4,394,430 and 4,323,634 crosslinked polymers, which in contrast to linear polymers are generally insoluble. Toners with the aforementioned crosslinked resins have tough physical properties, and thus are very difficult to subject to jetting processes.
There thus is a need for improved processes for obtaining crosslinked particles without jetting useful for the formulation of toner compositions that can be selected for imaging systems. Also, there is a need for dispersion polymerizations; and wherein there results toner particles of a diameter of from about 1 micron to about 20 microns without jetting. More specifically, there remains a need for toner compositions prepared by a dispersion polymerization process wherein the difunctional monomer or crosslinking component selected is formulated into a copolymer or terpolymer. Also, there is a need for processes that permit the preparation of toner compositions of a positive polarity, or a negative polarity without jetting. Moreover, there continues to be a need for generating particles by dispersion polymerization, without jetting and where the resulting toner compositions have low fusing temperatures, that is, less than about 150.degree. C.; and wherein the resulting charge enhancing additive stabilizer moiety is retained, and not leached from the toner composition. Also, there is a need for dispersion processes wherein jetting is eliminated, and there can be affected an optional chemical transformation of the stabilizer compounds by reactions with alkyl halides, organic carboxylic acids and organic alcohols, especially aliphatic alcohols, enabling the selection of the charge polarity for the resulting toner compositions prior to the preparation thereof. Additionally, there is a need for dispersion prepared crosslinked toner compositions with desirable admix charging properties, and appropriate triboelectric charging values permitting these compositions to be highly useful in xerographic imaging methods.